[NTG-context] Passing the name of an XML file to process via the command line

Hello list. I feel this should be an easy question to answer but I couldn't find a hint. I have a ConTeXt file which pulls in an XML file for processing using the command \xmlprocessfile{mydomain}{myXMLfile.xml}{} I would like instead to call context with the XML file name in the command line (so that I can use the same ConTeXt setups on multiple XML sources). How can I do that? Many thanks. Duncan